1. Field of the Invention
The present invention relates to heating selected areas of a laminated transparency, and in particular to an automotive windshield and a method of fabricating an automotive windshield for heating the lower portion of an automotive windshield where the windshield wipers reside when not in use.
2. Technical Considerations
Windshield wipers on motor vehicles typically are positioned along the lower portion of a windshield below the driver's field of vision. In extremely cold weather, it is possible that moisture in the air may freeze the rubber wiper blade to the glass surface of the windshield making the wipers inoperable. The wipers will have to be freed by hand or the vehicle must be heated to melt any ice holding the wipers to the windshield surface.
Several approaches have been used to heat the outer surface of a transparency. In U.S. Pat. No. 3,729,616 to Gruss et al.; U.S. Pat. No. 3,745,309 to Gruss et al.; U.S. Pat. No. 4,057,671 to Shoop; U.S. Pat. No. 4,078,107 to Bitterice et al.; U.S. Pat. No. 4,436,575 to Dran et al. and EP 385785 and 385791 to Lyon et al., the entire laminate is heated by a plurality of wires extending throughout the transparency. The wires are powered by busbars positioned along opposing edges of the transparency. In other arrangements, heat has been concentrated at the wiper rest area, i.e. the portion of the windshield where the wipers reside when deactivated. More particularly, in U.S. Pat. No. 4,373,130 to Krasborn et al., heating elements are positioned along the lower edge of the windshield behind a continuous, opaque heat absorbing layer so that the heating elements are not be visible from the front of the windshield. The elements are powered by busbars positioned along opposing edges of the windshield. In U.S. Pat. No. 5,173,586 to Gold, a metal strip is sealed against the outer surface of a windshield just below the wiper rest area. In U.S. Pat. No. 5,386,098 to Knudsen, a plurality of heating elements are secured to the inner surface of the windshield in the vicinity of the wiper rest area. The heating elements are powered by busbars with connection points at opposite corners of the windshield. In U.S. Pat. No. 5,451,280, electrically conductive ceramic enamel lines are formed behind the opaque ceramic band of the windshield in the wiper rest area. In JP 64-70222, a plurality of electrically conductive heating lines are printed on a major surface of one of the glass plies of a laminated window and extend along the wiper rest area of a laminate between a pair of opposing busbars. Still other heating arrangements include two separate heating systems: one to heat the upper central portion of the transparency and the other to heat the lower area in the vicinity of the wiper rest area. For example, in U.S. Pat. No. 4,109,133 to Hanle et al., upper and lower heating elements are screened on the surface of a rear window of a vehicle. In U.S. Pat. No. 4,971,848 to Ruelle et al., the lower portion heating elements of the heatable panel are screened on the glass surface in a mesh-like pattern. In U.S. Pat. No. 5,434,384 to Koontz, the upper and lower heating elements are transparent, electroconductive film coatings.
In each of these heating systems, the heating elements are either electrically conductive ceramic paints which are applied by a screening process and bonded to the glass surface and/or the heating elements are powered by busbars positioned along opposing edges of the transparency. Such systems require additional glass processing steps in order to incorporate the busbars and/or ceramic elements within the laminate. In addition, when the heating elements or busbars are applied to the glass or a component of the laminated windshield, any defects in the heating element require the glass or component to be scrapped or reworked.
It would be advantageous to provide a system for heating the windshield wiper rest area of a windshield to free the wipers frozen to the windshield that provides maximum flexibility as to the design of the heated area and minimizes any impact on the fabrication of the windshield.